Peptide YY (PYY) is a 36-residue peptide amide isolated originally from porcine intestine, and localized in the endocrine cells of the gastrointestinal tract and pancreas (Tatemoto et al. Proc. Natl. Acad. Sci. 79:2514, 1982). PYY shares a number of central and peripheral regulatory roles with its homologous peptide Neuropeptide Y (NPY), which was originally isolated from porcine brain (Tatemoto, Proc. Natl. Acad. Sci. 79:5485, 1982). PYY is localized in intestinal cells; NPY, in contrast, is present in the submucous and myenteric neurons which innervate the mucosal and smooth muscle layers, respectively (Ekblad et al. Neuroscience 20:169, 1987). Both PYY and NPY are believed to inhibit gut motility and blood flow (Laburthe, Trends Endocrinol. Metab. 1:168, 1990), and they are also thought to attenuate basal (Cox et al. Br. J Pharmacol. 101:247, 1990; Cox et al. J. Physiol. 398:65, 1988; Cox et al. Peptides 12:323, 1991; Friel et al. Br. J. Pharmacol. 88:425, 1986) and secretagogue-induced intestinal secretion in rats (Lundberg et al. Proc. Natl. Acad. Sci USA 79:4471, 1982; Playford et al. Lancet 335:1555, 1990) and humans (Playford et al., supra), as well as stimulate net absorption (MacFadyen et al. Neuropeptides 7:219, 1986). Elevated plasma PYY levels have been reported in individuals suffering from several conditions that cause diarrhea (Adrian et al. Gastroenterology 89:1070, 1985). Taken together, these observations suggest that PYY and NPY are released into the circulation after a meal (Adrian et al. Gastroenterology 89:1070, 1985; Balasubramaniam et al. Neuropeptides 14:209, 1989), and, thus, may play a physiological role in regulating intestinal secretion and absorption, serving as natural inhibitors of diarrhea.
A high affinity PYY receptor system which exhibits a slightly higher affinity for PYY than NPY has been characterized in rat intestinal epithelia (Laburthe et al. Endocrinology118:1910, 1986; Laburthe, Trends Endocrinol. Metab. supra) and shown to be negatively coupled to adenylate cyclase (Servin et al. Endocrinology 124:692, 1989). Consistently, PYY exhibited greater antisecretory potency than NPY in voltage clamped preparations of rat small intestine (Cox et al. J. Physiol. supra), while C-terminal fragments of NPY were found to be less effective in their antisecretory potency than PYY (Cox et al. Br. J. Pharmacol. supra). Structure-activity studies using several partial sequences have led to the identification of PYY(22-36) as the active site for interacting with intestinal PYY receptors (Balsubramaniam et al. Pept. Res. 1:32, 1988). PYY[3-36] is reportedly a selective ligand at the Y2 and Y5 receptors, which appear pharmacologically unique in preferring N-terminally truncated (i.e. C-terminal fragments of) NPY analogs.
PYY has been implicated in a number of physiological activities including nutrient uptake (see, e.g., Bilcheik et al. Digestive Disease Week 506:623, 1993), cell proliferation (see, e.g., Laburthe, Trends Endocrinol. Metab. 1:168, 1990; Voisin et al. J. Biol. Chem, 1993), lipolysis (see, e.g., Valet et al., J. Clin. Invest. 85:291, 1990), and vasoconstriction (see, e.g., Lundberg et al., Proc. Natl. Acad. Sci., USA 79:4471, 1982). Recently it has been suggested that infusion of normal postprandial concentrations of PYY(3-36) significantly reduces appetite and food intake in humans (see Batterham et al., Nature 418:656-654, 2002; Batterham et al., N Engl J Med. 349:941, 2003).
Peripheral administration of PYY reportedly reduces gastric acid secretion, gastric motility, exocrine pancreatic secretion (Yoshinaga, Mochizuki et al. Am J Physiol 263: G695-701, 1992) (Guan, Maouyo et al. Endocrinology 128: 911-6, 1991) (Pappas, Debas et al. Gastroenterology 91: 1386-9, 1986), gallbladder contraction and intestinal motility (Savage, Adrian et al. Gut 28: 166-70, 1987). The effects of central injection of PYY on gastric emptying, gastric motility and gastric acid secretion, as seen after direct injection in or around the hindbrain/brainstem (Chen and Rogers. Am J Physiol 269: R787-R792, 1995) (Chen, Rogers et al. Regul Pept 61: 95-98, 1996) (Yang and Tache. Am J Physiol 268: G943-8, 1995) (Chen, Stephens et al. Neurogastroenterol Motil 9: 109-116, 1997), may differ from those effects observed after peripheral injection. For example, centrally administered PYY had some effects opposite to those described herein for peripherally injected PYY[3-36] in that gastric acid secretion was stimulated, not inhibited. Gastric motility was suppressed only in conjunction with TRH stimulation, but not when administered alone, and was indeed stimulatory at higher doses through presumed interaction with PP receptors. PYY has been shown to stimulate food and water intake after central administration (Morley, Levine et al. Brain Res 341: 200-203, 1985) (Corp, Melville et al. Am J Physiol 259: R317-23, 1990).
Pharmacological studies and cloning efforts have revealed a number of seven transmembrane receptors for the PP family of peptides, and these receptors have been assigned the names Y1 through Y6 (and a putative PYY-preferring receptor or Y7). Typical signaling responses of these receptors are similar to those of other Gi/G0-coupled receptors, namely inhibition of adenylate cyclase. It is apparent that there is a clustering of amino acid sequence similarity between Y1, Y4 and Y6 receptors, while Y2 and Y5 define other families. Other binding sites have been identified by the rank order of potency of various peptides. The NPY-preferring receptor has been termed Y3, and PYY-preferring receptors have also been shown to exist (putative Y7) (See Michel, Beck-Sickinger et al. Pharmacol Rev 50:143-50, 1998; and Gehlert, D. R. Proc Soc Exp Biol Med 218: 7-22, 1998).
The Y5 and Y1 receptors have been suggested as the primary mediators of the food intake response (Marsh, Hollopeter et al. Nat Med 4: 718-21, 1998) (Kanatani, A., Mashiko, S., Murai, N., Sugimoto, N., Ito, J., Fukuroda, T., Fukami, T., Morin, N., MacNeil, D. J., Van der Ploeg, L. H., Saga, Y., Nishimura, S., and Ihara, M. Endocrinology 141: 1011-6, 2000). The prevalent idea has been that endogenous NPY, via these receptors, increases feeding behavior. Some proposed therapies for obesity have been directed toward antagonism of NPY receptors, while therapies for treating anorexia have been directed toward agonists of this ligand family (see, e.g., U.S. Pat. Nos. 5,939,462; 6,013,622; and 4,891,357). In general, PYY and NPY are reported to be equipotent and equally effective in all Y1, Y5 (and Y2) receptor assays studied (Gehlert, D. R. Proc Soc Exp Biol Med 218: 7-22, 1998). The main characteristic of putative Y3 receptors is that they recognize NPY, while PYY is at least an order of magnitude less potent. The Y3 receptor represents the only binding site/receptor shown to have a preference for NPY.
There is an additional binding site/receptor which shows preference for PYYs, termed PYY-preferring receptor. Different rank orders of binding to this receptor, or class of receptors, have been reported, suggesting that there may be more than one receptor in this family. In most cases it has been applied to describe a receptor where PYY was three to five times more potent than NPY. For purposes of this disclosure, reference to pharmacology of a PYY-preferring receptor means a receptor having any degree of preference for PYY over NPY.
Obesity and its associated disorders are common and very serious public health problems in the United States and throughout the world. Upper body obesity is the strongest risk factor known for type 2 diabetes mellitus, and is a strong risk factor for cardiovascular disease. Obesity is a recognized risk factor for hypertension, atherosclerosis, congestive heart failure, stroke, gallbladder disease, osteoarthritis, sleep apnea, reproductive disorders such as polycystic ovarian syndrome, cancers of the breast, prostate, and colon, and increased incidence of complications of general anesthesia. (see, e.g., Kopelman, Nature 404: 635-43, 2000). It reduces life-span and carries a serious risk of co-morbidities above, as well disorders such as infections, varicose veins, acanthosis nigricans, eczema, exercise intolerance, insulin resistance, hypertension, hypercholesterolemia, cholelithiasis, orthopedic injury, and thromboembolic disease (Rissanen, Heliovaara et al. BMJ 301: 8357, 1990). Obesity is also a risk factor for the group of conditions called insulin resistance syndrome, or “Syndrome X.” The pathogenesis of obesity is believed to be multifactorial but the basic problem is that in obese subjects nutrient availability and energy expenditure do not come into balance until there is excess adipose tissue. Obesity is currently a poorly treatable, chronic, essentially intractable metabolic disorder. Thus there remains a need for therapeutic drugs useful in weight reduction of obese persons.